This invention relates generally to flat panel display devices and particularly to an electron beam convergence and scanning structure for such devices.
Prior art flat panel display devices include a baseplate and a faceplate which are held in a spaced parallel relationship by a plurality of external sidewalls. A phosphor screen is arranged on the inside surface of the faceplate to produce a desired image when struck by electrons. The envelope is divided into a plurality of channels by internal support walls which also provide support against collapse because of atmospheric pressure. Each of the channels includes a beam guide structure along which electron beams propagate the lengths of the channels until one line of the visual display is to be produced. The electron beams are simultaneously ejected from propagation along between the guide mesh structures in all channels and travel toward the screen. When a color display is to be produced, each of the channels includes three electron beams which are individually modulated with the red, green and blue video information. As electrons travel toward the screen, they are converged to meet at a shadow mask which is spaced a preselected distance from the screen. The electron beams also are scanned transversely across each of the channels so that each channel produces a particular portion of the total horizontal line. U.S. Pat. No. 4,131,823 to T. L. Credelle discloses an electron beam convergence structure in which convergence electrodes are placed on the sides of the internal support walls. U.S. Pat. No. 4,117,368 to F. J. Marlowe et al. discloses a structure for transversely scanning the electron beams across the channels in which deflection electrodes are placed on the inside surfaces of the internal support walls. U.S. Pat. No. 4,330,735 to M. A. Leedom discloses a beam guide structure for a flat panel display device in which the meshes of the beam guide assemblies are held in the desired spaced parallel relationship by a plurality of insulative beads.
The convergence structure described in the Credelle patent and the beam scanning structure disclosed in the Marlowe et al. patent both are satisfactory for the purposes intended, however, in both of these systems the convergence and scanning electrodes are placed onto the internal support walls. Accordingly, because the convergence and scanning electrodes extend the full length of the channels, the glass from which the support walls are made must be flat to very close tolerances to assure uniform convergence and deflection along the full channel length. Additionally, the electron beams travel parabolic trajectories between the beam guide and the screen. As known to those skilled in the art, this results in a short distance between the deflection center and the screen. This leads to a larger spot on the screen which can cause color impurities. Also fringe fields from the scanning electrodes can affect color purity at the boundaries of the channels. The fringe fields can also cause color convergence errors in the longitudinal and transverse directions.
The present invention overcomes these difficulties by the provision of an electron beam convergence and scanning structure which is separate from the internal support walls and which provides localized scanning in the proximity of the beam guides.